1. Field of Invention
The present invention relates to a tape measure, and more particularly to a strengthened blade retractable tape measure, wherein the ruler blade, having a predetermined curvature, is adapted to rigidly extend at least 10 feet from the tape casing in a self-sustaining manner without buckling by its own weight, so as to substantially lengthen the measuring distance along the measuring blade.
2. Description of Related Arts
Retractable tape measures have been commonly used in commercial. A conventional retractable tape measure generally comprises a tape casing, a retractable reel assembly rotatably supported in the tape casing, and a ruler blade having an inner end attached to the retractable reel assembly such that the ruler blade is adapted to fold in the tape casing in a coil manner and to extend from the tape casing for length measuring purpose.
There are two major features of the retractable tape measure for professional use, especially for construction. One of the features of such retractable tape measure is to provide the ruler blade having a predetermined length to lengthen the measuring distance along the ruler blade. Another feature of the retractable tape measure is to provide the ruler blade that the ruler blade must be rigid enough to self-sustaining manner when the ruler blade is extended from the tape casing. Therefore, the user is able to self-operate the retractable tape measure to measure the distance. In other words, the size and the weight of the retractable tape measure is not the most important concern for the professionals.
In order to accomplish the above features of the retractable tape measure, the dimension of the ruler blade must be configured. The width of the ruler blade can be substantially increased for enhancing the self-sustaining support of the ruler blade. However, the length of the ruler blade will be shortened to remain the weight thereof constantly. Alternatively, the curvature of the ruler blade can be increased to enhance the self-sustaining ability thereof. However, the ruler blade cannot be smoothly retracted back to the tape casing.
Accordingly, U.S. Pat. No. 6,324,769, owned by Murray, generally suggests a tape measure comprising a ruler blade having a width in the flattened configuration thereof having a dimension within the range of 1.10″–1.5″, a height in the concave-convex configuration thereof having a dimension within the range of 0.25″–0.40″, and a thickness in either configuration thereof having a dimension within the range of 0.0045″–0.0063″, such that the ruler blade is capable of standing out from the tape casing with a measuring length at least 10.5 feet.
Unfortunately, the Stanley case only provides a general measuring scope to achieve a 10.5 ft self-sustaining extending length. For most users and manufacturers, figuring out an optimal ruler blade size based on such an ambiguous scope is still a hassle. This is due to the fact that not all size combinations within the Stanley's scope are effective. For instance, in a user chosen a ruler blade with such size combination, a 1.38″ (35 mm) width, a 0.25″ (6.35 mm) height, and a 0.0063″ (0.16 mm) thickness, the 10.5 ft self-sustaining extending length would still be unreachable. It is noted the thickness 0.0063″ is already increased to the ceiling of the Stanley's scope.
In other words, the self-sustaining extending length of a ruler blade is not only determined by the above mentioned dimensions such as the width, the height and the thickness of the ruler blade. More importantly, a concave-convex curvature structure of such ruler blade is by far the most contributive factor to ensure the ruler blade extended out from tape casing at least 10 feet with a sustained manner. An optimal curvature of the concave-convex configuration is a key point to ensure standing firmness and rigidity of the ruler blade whenever the ruler blade is extracted out from the tape casing. Seemingly, a bigger curvature is desirable to guarantee the extended ruler blade self-sustained in position. Unfortunately, the ruler blade with a bigger curvature would cause applicable problems. This is due to the fact that the curved ruler blade is difficult to be reeled back into the tape casing.
Furthermore, the curvature of the ruler blade is preset during a tooling process. That is to say, once the ruler blade is reduced into products, the curvature is unchangeable. Therefore, the modification and improvement of the ruler blade should be considered as one of the important subject matter of the retractable tape measure to enhance the practice use thereof.